Introduction

The Binoreille project targets deaf people from one ear. The device allows the sound to be received from the side of the deaf ear and is transferred to the functional ear. In this prototype, the equipment consists of a headset and a box containing electronics for sound processing.

The first version was built during the "Abilympics 2016" in Bordeaux. Simon Juif had proposed a solution using a teensy electronic card which is powerfull and small enough for future miniaturization. The limit we had then encountered concerned the listening device, a basic headphone fitted on the top of the ear for not preventing the functional ear to hear its environment on its side.

By understanding the designs, plans, components or assemblies related to My Human Kit prototypes, I understand and agree that any information or material indicated by anyone associated with a design team is released as is without any warranty of any kind and is intended to be shared for the purpose of replicating, modifying or improving the plan. I understand that these prototypes aim to develop alternative open source solutions for people with disabilities. I understand and agree that any person associated with My Human Kit could not be responsible for any injury or damage resulting from the manufacture or use of these prototypes.

Operating principle and choice of headphone

In order to not disturb the hearing of the hearing ear, the chosen headphone is a bone-conduction one which is placed on the temple rather than in the hollow of the ear. A small microphone fixed on the headphone, on the side of impaired hearing leads the received sound towards the hearing ear, after treatment.

Bone conduction

Bone conduction is an alternative form of hearing. The sound emitted through the transducer of the headphone is transmitted through the skull until intern organs of hearing, without going through the ear drum.

Operating principle

The outside sound is picked up on the side of the damaged ear through an electret microphone. This microphone transforms the accoustic signal into electric signal, which is filtered in a first circuit in order to limit interference signals and adapt the voltage level. Then, the signal goes in the mic input of the audio card to receive a digital processing.

Three successive filters are applied on the signal: a high pass filter at 300 Hz, a low pass filter at 12000 Hz and a variable band pass filter defined by two poteentiometers: frequency (for the central frequency), width (to define the width of the frequency range). The third potentiometer adjusts the volume towards the headphone.

This prototype is based on a Teensy 3.2 microcontroller card.

Prerequisites

Arduino environnement should be installed.

Know how to use a 3D printer

Know how to use a lasercut machine

Know how to weld

Prototype

During the making of the prototype at the Fabrikarium in October 2016, the following versions of software were used:

audio adapter “audio shield rev.b”

Teensy v3.2 microcontroller

Arduino IDE version 1.6.12

Teensyduino version 1.30

Teensyloader version 1.15

3D printer Bicephale Mark One

Laser cutter Trotec

Download

Welding the components

Prepare the components in the following order:
- Weld the two female pin headers (14 pins) on the audio adapter.
- Weld the female pin headers (2 pins) on the mic input of audio adapter.
- Weld the two male pin headers (14 pins each) on the teensy card.
- Weld the female pin header (4 pins) on the regulated output power for the potentiometers.

Preparation of the audio adapter for teensy

1- Solder the two female pin headers (14 pins) on the audio adapter.
2- Solder the female pin headers (2 pins) on the mic input of audio adapter. (2 pin headers are enough although we can see 3 on the picture)

Preparation of the Teensy

Pin header on the regulated power output of the Teensy

4-Prepare the female pin header (2X4 pins) linking all pin headers together with a conductive wire.
Then solder the female pin header (2X4 pins) on the regulated output power 3.3V for the potentiometers, and the Ground next to it.

Preparing the 3 potentiometers

1- Cut 3 wires of about 7 cm length.
2- Use a wire cutter to remove sleeving and free the wires on 1 cm length.
3- Tin bare ends to eliminate fraying.
4- Solder the wires on the 3 potentiometers as shown on the picture below

Preparing the electret microphone

Use a cutter to remove sleeving and free the wires from the mono shielded cable. Use a stripping pliers to remove sleeving of the little wire inside. Tin each side of the little wire and tin also the copper wire on each side after having rolled it on itself. Solder the copper wire on the (-) of electret microphone and the little wire on the (+) of the electret microphone.
The microphone is ready to use.

Free the wires

Use a cutter to remove sleeving and free the wires from the mono shielded cable. Use a stripping pliers to remove sleeving of the little wire inside.

Tin

Tin each side of the little wire and tin also the copper wire on each side after having rolled it on itself.

Weld

Solder the little wire on the (+) of the electret microphone.

souder

Solder the copper wire on the (-) of the electret microphone.

microphone ready

Remove sleeving and free the wires from the mono shielded cable on the other side, and tin it as shown in the above steps.
The microphone is ready.

Filter circuit

In order to reduce stray sounds due to the microphone cable length, it is recommended to add a filter.
Get some stripboards (veroboard, 8x8 holes)
Solder the filter circuit as shown below (the cable is long and has an antenna effect. This filter reduces stray sounds and reduces the voltage with a voltage divider before going to the audio adapter).

Filter connexions

Connect the filter to the Teensy card by refering to the schematic below.

Connect also the microphone (+) on the mic input of the audio adapter and the ground of the mic (-) on the ground input next to the mic input (+) of the audio adapter.

Add a button ON/OFF with the SPST (switch) between the ground of battery (-) and the ground of the Teensy as shown on the schematic.

Assembly diagram : Teensy+ Audio adapter + other components

Stack the Teensy card on the audio adapter as indicated on the following diagram.
The ON/OFF switch is not drawn on this diagram as it was added after the drawing.
Then plug the potentiometers and the battery as shown above.

Installation of Teensyduino and Arduino configuration in order to load the program on the Teensy card

Glue all elements together except the covert to constitute a solid box.

Assembly

Fix the potentiometers.

Mounting the potentiometers

Mount the potentiometers as shown in the image.

Mounting the potentiometers

Add nuts and washers on the outer side . Tighten it with a wrench holding the potentiometer on the inner side.

Mounting the potentiometers

Repeat the operation for the three potentiometers.

Mounting the potentiometers

Global view

- Set up the battery on the bottom of the enclosure.
- Fix the circuits on a little wood panel and set it up on the battery with double-sided foam tape.
- Plug the headphone on the output of audio adapter.

Safety precautions

Congrats! The build is done and you can test the prototype. In order to prevent your audition from any trouble, it’s necessary to pull down the volume at the maximum before you plug the prototype on the battery. You can then adjust the volume slowly at your convenience.

You can use this prototype by fixing the microphone on your sleeve for example, or holding it in your hand keeping it at a safe distance of minimum 20 cm from the headphone. Please carry outtheses security tips, else you could damage your hearing!

Issue to solve before fixing the support on the headphone: We tested an integration of the microphone on the headphone but this prototype is still under development, and we have not yet resolved the larsen issue triggered in this configuration.

We would be pleased to collect your feedback and your observations as well as your possible improvements that we could include in this tutorial. So, please don’t hesitate to contact us 🙂

3D printing of the microphone support in order to fix it on the headphone

This 3D model is a support designed for electret microphone MCE-100 which is supposed to be fixed on the headphone Aftershokz Sports M3, when the larsen issue will be fixed.

This modelisation was created by Jérôme Terrier during the Fabrikarium in october 2016 specially for the Binoreille prototype.

The intégration of the microphone on the headphone represents actually a danger for the hearing for the reasons mentionned aboved. It is supposed to be tested with caution and only if you have a solution to prevent the larsen.